The present invention relates to blends of olefinic polymers and vinyl aromatic polymers. Compatibilizers, usually some type of rubber copolymer or graft rubber copolymer, are necessary third ingredients in order to facilitate mixing of the olefinic polymers with the vinyl aromatic polymers. It is desirable to blend such components in an attempt to obtain the thermoforming properties of vinyl aromatic polymers and the strength properties, especially impact strength, of olefin polymers.
Polystyrene and high density polyethylene blends have good thermoforming properties. Under some circumstances, they also show good impact strength. However, when they are extruded, the resulting extruded products exhibit oriented strength properties. Impact strength is good in a direction transverse of the direction of extrusion (sometimes referred to herein as the cross directions). However, in the direction of the extrusion, i.e., the machine direction, impact strength is very poor.